A royal expert and author is speaking out this week to reveal why Kate Middleton is so popular among aides working at the palace.

“Everyone that I have spoken to confirms that Kate is a very warm, but also a very calm and a very kind person,” royal expert Tom Quinn said to Fox News. “… I think she’s very strong, but she’s very conscious, very kind to the people who work for her.”

Quinn just released his new book “Kensington Palace: An Intimate Memoir from Queen Mary to Meghan Markle,” in which he spoke to numerous people who have worked at the palace over the years. He was a bit surprised to find that not a single person had anything bad about Kate, who is married to Prince William and is mother to his three children.

Quinn explained that Kate has been a stable presence for William at a time in his life when he desperately needed this, as he met her just a few years after the 1997 death of his mother, Princess Diana.

“Kate has been a perfect [companion] because she’s so calm and stable — and that’s what he needs,” Quinn said. “I’m not saying she’s sort of a second mother, but there’s an element of that. She’s… a rock. It’s a bit of a cliche, but she’s someone who just doesn’t have a history that’s all over the place. She’s very calm, very rational. And I think that’s why the royal family feels safe.”

“She also does something which is absolutely key to being happy while also being a member of the royal family,” he added. “Whatever the press may say about you, you don’t complain and you don’t explain. And Kate is very good at that.”

Sarah Gristwood, author of “Elizabeth: The Queen and the Crown,” agreed with Quinn’s assessment of Kate.

“Those who know her say there is a real core of strength, and she did set her mind to the job,” Gristwood told People magazine last week. “But at the same time, she’d had to be superhuman not to feel the pressure.”

Royal etiquette expert Myka Meier also opened up about the pressure that Kate is facing as someone who will be queen someday.

“The future queen is a role model to the U.K. but also to the world, which means all eyes are on you,” Meier said. “The added pressure of having cameras everywhere to catch even the slightest eye movement makes everything she does a conscious effort. From the perfectly poised posture to the way she descends a staircase or gets out of a car — it is all carefully done.”

“I think the pressure is more about her public image, making sure she is wearing the right brands, showing the kids in less expensive clothing, especially right now,” added another insider. “Small details, but they matter.”

All palace insiders seem to agree that Kate is someone who never lets the pressure show, regardless of how intense it gets.

“Catherine is the sort of woman who will take on whatever she needs to,” a close friend of hers said. “If she needs to step up to the plate, she does it — and she always has.”